1. Field of the invention
The present invention relates to a magnetic recording and reproducing device which can record and reproduce a discriminative signal.
2. Description of the Prior Art
In the audio field, recently many practices have been made to convert the audio signal from an analog form to a digital form when recording, and convert the signal back to an analog form when reproducing, so as to obtain a high fidelity recording and reproducing. Since it is simple to combine and separate signals when an analog audio signal is converted to a digital signal, it is advantageous to employ the digital audio signal recording in the field of video tape recorder such that the digital audio signal and video signal are recorded simultaneously. A typical video tape recorder has two heads alternately scanned along a magnetic tape, one head thereby recording (or reproducing) video signals of even fields, and other head recording (or reproducing) video signals of odd fields. Therefore, while one of the two heads is in use for recording (or reproducing) the video signal, the other is not in use. If this other head, which is not in use, can be used for recording (or reproducing) the digital signal, then the digital signal recording (or reproducing) can be carried out with a high efficiency.
To this end, it is suggested, as shown in FIGS. 1a and 1b and also disclosed in U.S. Pat. No. 4,303,950 to Taniguchi et al., that the magnetic tape 4 wound around the cylinder 1 should extend angularly more than 180.degree. around the cylinder 1, thereby covering the two heads 2 and 3 at the same time. When the arrangement as shown in FIG. 1a is employed, the signal alignment in the time domain with respect to the scan of heads 2 and 3 is shown in FIG. 2a, and the actual signal alignment on the magnetic tape 4 is shown in FIG. 3a. And, when the arrangement as shown in FIG. 1b is employed, the signal alignment in the time domain with respect to the scan of heads 2 and 3 is shown in FIG. 2b, and the actual signal alignment on the magnetic tape 4 is shown in FIG. 3b. In FIGS. 2a, 2b, 3a and 3b, shaded sections show areas where digital audio signals are stored, each shaded section containing the digital audio signal for 1 field. Such a shaded section is located in front of, or in back of, each span of section where a video signal of 1 field is recorded.
As shown in FIG. 4, the audio digital signal for 1 field comprises a plurality of frames aligned in series, and each frame comprises a block including a plurality of sample data aligned in series for the purpose of error correction, and having a sync signal and an error detecting signal provided, respectively, at opposite ends of the block. The digital signal may be further provided with a discrimination signal in a digital form, as shown in FIG. 4, for the purpose of signal processing and effecting various controls. Such a discrimination signal may contain information as to the time and/or field number, thereby giving access to a required video signal, or may contain information as to whether the audio signal is in a stereophonic form or in a monophonic form.
It is to be noted that the discrimination signal shown in FIG. 4 is located in front of the audio signal of 1 field, but can be divided into pieces and distributed in a plurality of frames.
From the practical point, the discrimination signal is not an indispensable signal and, therefore, it is better to leave the choice as to whether or not to use the discrimination signal to the user, because when compared with the case wherein the discrimination signal is not needed, the arrangement of the device will have much freedom such that a circuit for detecting the discrimination signal can be simplified or eliminated.
However, in order to have a compatibility with a tape which has been recorded, it is necessary to record the discrimination signals at predetermined locations in the tape. And, in a device which does not utilize the discrimination signal (hereinafter referred to as a non-discriminative type device), it is necessary to record, during recording, a signal indicating that the discrimination signal, is invalid. Contrary, in a device which utilizes the discrimination signal (hereinafter referred to as a discriminative type device), it is necessary to detect, when reproducing a tape having invalid discrimination signals, that the discrimination signal is invalid.